It is known in the art relating to reciprocating piston machines, and in particular multicylinder piston engines, to provide suitable auxiliary balancing devices to counterbalance unbalanced primary and secondary forces applied to the crankshaft by reciprocating components associated with the various engine cylinders. While some engine cylinder and crank arrangements provide inherent balancing of primary and secondary vibrations, many common arrangements result in unbalanced forces which cannot be offset by weights added to the crankshaft.
For example, a conventional crank arrangement for a four cylinder in-line piston engine provides substantial balance of primary forces and primary and secondary couples but yields a resultant unbalanced secondary shaking force. This shaking force reciprocates at twice crankshaft speed in the plane of the cylinders and crankshaft and in a direction perpendicular to the crankshaft axis, being centered longitudinally midway between the cylinders and, generally, at the center main bearing bulkhead supporting the crankshaft.
Such unbalanced secondary shaking forces may be balanced, if desired, by a balancing mechanism properly located having one or more pairs of counterweights rotated in opposite directions at twice crankshaft speed to provide a reciprocating shaking force directed oppositely to the unbalanced secondary shaking force of the engine. Such "add on" balancers generally require additional space, in the engine housing or external to the engine, with appropriate driving mechanisms which may add undesired complexity and weight to the engine construction as well as requiring additional space in the engine compartment.